Add versionadded remarks

Author: mpdude

reference/forms/types/form.rst

@@ -86,6 +86,10 @@ the underlying object that will be used to populate the form field.
 
 More details are available in the section on :doc:`/form/data_mappers`.
 
+.. versionadded:: 5.2
+
+    Form mapping callbacks were added in Symfony 5.2.
+
 .. include:: /reference/forms/types/options/help.rst.inc
 
 .. include:: /reference/forms/types/options/help_attr.rst.inc
@@ -132,6 +136,10 @@ back to the underlying object.
 
 More details are available in the section on :doc:`/form/data_mappers`.
 
+.. versionadded:: 5.2
+
+    Form mapping callbacks were added in Symfony 5.2.
+
 .. include:: /reference/forms/types/options/trim.rst.inc
 
 .. include:: /reference/forms/types/options/validation_groups.rst.inc